The advent of optical transmission in telecommunication systems has brought with it a need for power supplies that are capable of delivering to a load a voltage that is, within a close tolerance range, equal to a specified value. With optical transmission systems operating at ever higher transmission rates, conventional power supplies whose output voltage is controlled to within ±5%, or even ±10%, are not accurate enough. Such power supplies have proved unsuitable in, for example, 40 Gb/s transmission systems which use ultra-sensitive laser components, high speed modulator drivers, chips having a 2.5 Gb/s core frequency, and 20 Gb/s oscillators and power amplifiers, by way of example. Such transmission systems and their components and devices typically require supply voltages having a tolerance of ±2% over the lifetime of the system and under a wide range of normally expected environmental conditions.
As a practical matter, known power supplies cannot provide an output voltage having a tolerance of ±2% unless certain highly accurate and expensive components are used along with elaborate and expensive filtering and shielding. Even with these precautions, however, the effects produced by the aging of components are difficult, if not impossible, to counteract.